1. Field of the Invention
The present invention relates to high-field permanent magnet flux sources. More specifically, it relates to a temperature compensating means for use with permanent-magnet flux sources such as magic spheres and the like.
2. Description of the Prior Art
Magic spheres, toroids, igloos, rings and similar compact magnetic structures have been developed for use as high magnetic field sources that do not need an electric power supply. Such unusual magnetic structures were made possible by the advent of rare-earth permanent magnets which have significantly high remanences and coercivities.
U.S. Pat. No. 4,837,542 describes a typical magic sphere. U.S. Pat. No. 4,839,059 discloses a magic ring for use in a wiggler or a twister. Further details of these and similar permanent magnets are disclosed in the papers entitled A Catalogue of Novel Permanent Magnet Field Sources by H. A. Leupold, et al., Paper No. W3.2 at the 9th International Workshop on Rare-Earth Magnets and Their Applications, Bad Soden, FRG, 1987; and IEEE Transactions on Magnetics, Vol. MAG-23, No. 5, Sept. 1987, pp. 3628-3629.
Although such high-field magnets have served the purpose, they have not proved entirely satisfactory under all conditions of service for the reason that considerable difficulty has been experienced in maintaining a constant working magnetic field under temperature changes in temperature-sensitive magnets. More specifically, it has been known for some time that magic spheres can produce very large working fields in a relatively large cavity with relatively small structural bulk. For example, a magic sphere four inches in diameter can produce a working magnetic field of 20-30 kilogauss (kG) in a cavity that is one inch in diameter.
It has been known that rare earth permanent magnets of the type discussed above can produce very high fields that may be in excess of the remanence of the magnetic material used. For some applications, it is very important that the working fields remain constant to a very high degree of precision, e.g. within a few parts per million. In some instances chemically temperature-compensated magnets have been used for this purpose. However, this solution is not entirely satisfactory because chemical compensation often entails considerable loss in magnetic remanence with a proportional decrease in field strength. To prevent the latter, more material is used to compensate for the remanence loss, thereby creating greater bulk.
Consequently, there has been a need for improvements in the design of magic spheres, toroids, igloos, rings and like permanent magnet flux sources to render such devices less sensitive to temperature changes.